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WALTER E. DENNISON, OF SAN FRANCISCO, CALIFORNIA, ASSIGNOR TO THE CITY STREET IMPROVEMENT COMPANY, OF SAME PLACE.

METHOD OF SURFACE-FINISHING FOR ASPHALT 0R BITUMINOUS PAVEMENTS.

SPECIFICATION forming part of Letters Patent No. 600,215, dated March 8, 1898.

Application filed December 18, 1896.

To all whom it may concern.-

Be it known that I, WALTER E. DENNISON, a citizen of the United States, residing in the city and county of San Francisco and State of California, have invented certain new and useful Improvements in Methods of Surface- Finishing for Asphalt or Bituminous Pavements, of which the following is a specification.

My invention relates to an improvement made in finishing the surface of bituminous pavements to prevent wear and increase their durability.

'It is well known that in the construction of pavements from asphaltum and bituminous materials, no matter how well the material is prepared and how carefully laid, the surface becomes softened, checked, and worn in ruts under the traflic of teams and the effects of the weather. In some instances, also, the material deteriorates and loses its qualities by the liberation of the free oils or tar which, being drawn out and worked out by heat and the travel of horses and vehicles, is washed off into the gutters. To overcome these defects and objections and produce a firm and durable wearing-surface is the object of my present invention; and to such end my improvement consists, essentially, in producing a smooth hard-finish wearing surface on asphalt and bituminous pavements by first covering the surface of the pavement after it is laid in place with a layer of infusorial earth and afterward ironing the same with heated irons, substantially as hereinafter described, and pointed out in the claim.

My invention is based on the discovery I have made that by spreading upon the surface of an asphalt or a bituminous pavement after it is laid and finished a layer of the material or substance known as infusorial earth (the analysis of which is as follows: silica, 69.38; oxid of iron, 8. 94:; alumina, 11.72; organic matter, 7.69; undetermined, 1.64; total, 99. 37) and then rubbing and ironing the said layer with heated irons, such as are used at the present time upon the bituminous material in the operation of forming the pavement itself, a smooth hard-finish surface will be formed and produced having certain quali- Serial No. 616,210. (No specimens.)

and portions of irregular or uneven surface a pavement thus treated will wear evenly and preserve a uniform1y-smooth surface for a considerable period of time.

The following description explains the nature of my said improvement and the manner in which I proceed to apply, use, and carry out the same.

In the work of constructing or laying pavements of asphalt or bituminous rock the material or substance when disintegrated and softened by heat is spread to the thickness of two or three inches upon a bed or foundation of concrete previously laid, and the material is brought to a close homogeneous condition aft-er it is spread by means of heated rollers and irons applied to and worked over successive layers of the material until the required thickness or depth of the asphalt or bitumen is obtained. This is the usual method at the present time followed in forming a pavement of this character. Upon the surface of such pavement, after the same is finished smooth and level, I spread a layer of the substance or. material known as infusorial earth by first reducing a quantity of such material to powder and sifting it over the asphalt or bituminous surface, and then by means of heated irons it is worked into such surface and brought into a smooth and hard condition and of a uniform depth or thickness.

The substance or material known as infusorial earth can be obtained in large quantities from many localities in a condition ready for use without any treatment other than pulveriziug the lumps to reduce it to powder. Its especial value as a material for this purpose appears to be due to its composition,

which is principally silica and alumina, and to the absence of lime as an ingredient or element, in which last-mentioned respect it dif fers from other materials and mixtures containing or composed principally of lime in different forms that have heretofore been suggested and to some extent used as a surface dressing or finishing for pavements of asphalt and bitumen. Its advantages over such material composed of or containing lime appear to be its property of resisting the eifects of the weather Without deteriorating or undergoing any chemical changes and of remaining unaffected. by extremes of temperature, thereby retaining the desirable qualities of hardness and firmness of surfaceeven when exposed to heavy traffic and cansin g the pavement to Wear evenly.

Having thus fully described my invention, What I claim as new, and desire to secure by Letters Patent, is

That improvement in surface finishing pavements of asphalt or bituminous rock which consists in spreading over the surface 7 of the pavement after the material composing WALTER E. DENNISON. [n s.]

Witnesses:

O. W. M. SMITH, ALFRED A. ENQUIST. 

